Method of heat treating



PatentedJan. 23, 1940 UNITED STATES METHOD OF HEAT TREATING Vincent '1'. Malcolm, Indian Orchard, Mass, as-

aim: to The Chapman Valve Mtg. 00., Indian Orchard, Mesa, a corporation of Massachu- No Drawing. Application August 31, 1938, Serial No. 227,763

2 Claims.

This invention relates to improvements in the method of treating alloy steels.

The principal objects of the invention are directed to the provision of an improved method of treating ferritic steels so as to provide a hard case and a relatively soft, ductile core.

Steels of the type to which the invention relates have been subjected to heat treating operations involving quenching and they subsequently showed a Brinnell hardness of but 500 and had a relativelyhard core. As contrasted with these results, by means of my invention, an extremely hard case has been produced on the same steels, ,one showing 900 to 1100 Vickers Brinnell yet having the desired relatively soft, ductile core,

This invention is particularly concerned with ferritic chrome steels which range in chromium content from two to fourteen percent and contain in addition either molybdenum, vanadium or tungsten or combinations of them.

Examples, stated in percentages, of the combinations within the range of alloys coming within the invention are as follows:

u Per cent Chromium 1.5 to2.25 Molybdenum .4 to .6 Silico .5 to 2.

Manganese .3 to1.

Sulphur, maximum .06 Phosphorus, maximum .06 Carbon .05to .5

I Per cent Chromium 4. to 6. Molybdenum .4 to .6

Or tungsten .8 to 1.25 Silic n .5 to 2.

0 Manganese .3 to 1.

- Sulphur, maximum .06

Phosphorus, maximum .06

Carbon .05to .5

Per cent Chromium 10 to 14 Silicon .2 to 1.0 Manganese .3 to 1. Sulphur, maximum .06 Phosphorus, maximum .06 Carbon .05to .5

In the practise of the invention, the steel to be treated is placed in a container which is subll stantially closed and the container is placed within a heating furnace for heating the steel. The temperature employed will be such that the steel is heated within a range from about 900 to 1700 F.

While the work is thus being heated, the prodl nets of ammonia gas are led into the container so as to contact with the steel. Prior to entering the container, the ammonia gas is preferably passed successively through scrubbing, drying, cracking and catalyzing units similar in construc- 10 tion and adapted for similar functions as the units shown and described in my pending application Ser. No. 143,419, filed May 19, 1937.

The units described function to scrub the gas, eliminate moisture, disassociate the important constituents, such as hydrogen and nitrogen, and activate a certain element or elements of the gas.

The resultant ammonia gas products are then led to the steel in the closed compartment as stated while heat is maintained within the temperature range stated for a period of one-half hour or more. This may be called the initial step.

At the end of the initial treating step, the flow of ammonia gas is cut oil ahead at least of the cracking unit, and preferably ahead of the scrubbing unit, and is conducted direct from the supply thereof to an ionizing unit and thence into the compartment containing the steel. v

The temperature employed for what may be called the final step is in a range from 850 to 1400" F. and preferably in the neighborhood of 1100 F. The duration of the final treatment is relatively longer than that for the initial treatment and may range from 4 hours to 50 hours or more. The time of treatment will depend upon the size, shape and, to some extent, the characteristics of the steel being treated, as well as upon thespecific results desired.

During the final step of the process substantially nascent nitrogen is delivered to the compartment containing the steel being treated so that by maintaining the desired operating temperature the nitrogen combines with and acts on certain constituents of the steel to provide an extremely hard case whilst the core of the steel 45 remains, or is rendered, relatively soft and ductile.

While I have described the invention in great detail and with respect to the present preferred form thereof, it is not desired to be limited I50 thereto since many changes and modifications may be made therein without departing from the spirit and scope of the invention. What it is desired to claim and secure by Letters Patent of the United States is: 6

1. The process of heat-treating chrome-ferritic steels containing a relatively slight amount of nickel if any which consists in, enclosing the steel to be treated in a closed container, heating the steel to a temperature within the range of from 900" F. to 1700" F., flowing ammonia gas from a supply thereof into and through cracking and catalyzing units and then into said container, continuing the heating of the steel in the presence of the ammonia gas constituents at a temperature within said range for a period 0! at least one halt-hour, then cutting of! the flow of said ammonia gas into said container and causing it to flow into and through an ionizing unit and then into said container. and finally heating the steel in the presence of the ammonia gas constituents to a temperature within the range 0! from 850' F. to 1400 F. for a period of from four to fiIty hours. 4

2. The process of heat-treating chrome-territic steels containing a relatively slight amount of nickel if any which consists in. enclosing the steel to betreated in a closed containenheating the steel to a temperature within the range of from 900 F. to 1700 F.. flowing ammonia gas from a supply thereof successively into and through scrubbing, drying, cracking, and catalyzing units and then into said container, continuing the heating 0! the steel in the presence of the ammonia gas constituents at a temperature within said range for a period of at least one half-hour, then cutting oi! the flow oi said ammonia gas between said supply and said container and at least ahead of said cracking unit and causing it to flow into and through an ionizing unit and 1 then into said container, and finally heating the steel in the presence of the ammonia gas constituents to a temperature of approximately 1100 I". for a period of from four to nity hours.

' I VINCENT T. MALCOLM. 

